robot_localization: 2.1.6-0 in 'indigo/distribution.yaml' [bloom]

Increasing version of package(s) in repository `robot_localization` to `2.1.6-0`:

- upstream repository: https://github.com/cra-ros-pkg/robot_localization.git
- release repository: https://github.com/cra-ros-pkg/robot_localization-release.git
- distro file: `indigo/distribution.yaml`
- bloom version: `0.5.12`
- previous version for package: `2.1.5-0`

## robot_localization

```
* Added unscented Kalman filter (UKF) localization node
* Fixed map->odom tf calculation
* Acceleration data from IMUs is now used in computing the state estimate
* Added 2D mode
```